TriMet News

Plan Ahead! Triple digit temps to affect TriMet service

With extreme heat expected all week and some days expected to reach triple digits, TriMet reminds riders to prepare for the heat and stay hydrated. MAX trains will slow in some sections during high heat and system wide if temperatures soar above 100. Extreme temperatures also could slow or suspend WES Commuter Rail service.

MAX and WES runs slower in higher temperatures

90 degrees
When temperatures pass 90 degrees, TriMet reduces MAX speeds by 10 mph for all areas with speed limits of 35 mph and above. This may lead to delays, especially if temps soar early in the day.

95 degrees
WES has extreme temperature restrictions dictated by Portland & Western Railroad (PNWR). Per the PNWR policy, when temperatures exceed 95 degrees, WES will operate at a maximum authorized speed of 30 miles per hour.

100 degrees
If temperatures reach 100 or higher, we reduce all MAX speeds to no faster than 35 mph. This will lead to system wide delays. If the temperatures soar higher, train speeds may decrease even more.

105 degrees
If extreme temperatures soar to 105 degrees, PNWR will stop all heavy rail train service, which would mean WES service would be suspended and shuttle buses will provide service to WES stations.

Preventing system damage

Our goal is to keep riders safe. When temperatures start to rise, MAX trains slow down as a safety precaution. Rail temperatures can approach 20 to 30 degrees hotter than the ambient temperatures. Like in other cities, the MAX Light Rail system is designed for the average temperatures of our local climate. Also, every rail system has certain thresholds beyond the usual operating environment that force temporary changes in operations, be that low or high temperatures.

The overhead power wires may expand in extreme heat. Because copper expands more than steel, we have a system of pulleys with counterweights that tug on the wires to keep them tight. Sometimes, it gets so hot that the counterweights touch the ground and the wire starts to sag anyway. Trains run slower to prevent damage to the overhead wire as well as the pantograph or “arm” mounted on the roof of the train that runs underneath the wire.

In extreme heat, steel rails can expand requiring trains to run more slowly through the area to prevent damage. When many miles of rail are subjected to intense heat, the rail becomes incredibly hot. The stone track-bed and the consistent lack of shade add to the high temperatures. Since the rail is firmly anchored into the railroad ties, it has little room to move.

Heat causes expansion and the super-heated rail can increase in length measuring in several inches over a great distance. Since there cannot be any gaps in a rail to allow for this expansion, pressure builds up in the rail as it tries to expand lengthwise but cannot. With no room to expand, the rail can bow, known as a “sun kink” or “heat kink”.

Our operators have to watch for both sagging power wires and “sun kinked” rails when it’s very, hot outside. To be safe, they slow down to make sure nothing goes wrong. As it gets even hotter, they have to slow down more.

Buses and extreme heat

Some buses could experience some heat-related issues as any vehicle does that’s running for long hours in excessive heat.